Liquid gravity and weight gauge



Ocf- 12, 1954 c. A. DE GIE-Rs 2,691,296

LIQUID GRAVITY AND WEIGHTZGAUGE Filed Nov. 14, 1 949 3 Sheets-Sheet l ZM FicV-r'.

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BY fw/KM Oct. 12,' 1954 c. A. DE GIERs 2,59296 LIQUID GRAVITY AND WEIGHT GAUGE Filed Nov. 14. 1949 3 Sheets-Sheet 2 ATTORNEY.

Oct. l2, 1954 c. A. DE GIERS 2,691,296

LIQUID GRAVITY AND WEIGHT GAUGE Filed Nov. 14. 1949 3 Sheets-Sheet 3 FIG. 5.

|76/ PowER suPPLv |84 MEASURING CIRCUIT AMPLIFIER l 1NVENToR.

CLARENCE A. DEGIERS BYQ//m ATTORNEY.

Patenteci Oct. 12, 195.4

UNITED STATES FATENT OFFICE LIQUID GRAVITY AND WEIGHT GAUGE Application November 14, 1949, Serial No. 127,076

(Cl. i3- 32) 8 Claims. 1

This invention relates to means for measuring and indicating the specific gravity of liquids, and more particularly to apparatus in which the positions of a plurality of floats of diierent bulk specic gravities control the value of a predetermined electrical characteristic of an electrical element, which may be either a resistance or a reactance (either inductive or capacitive), the positions of the lioats being responsive to the specific gravity of the liquid under test. vIn the case of a variable reactance, its value may in turn control the series-resonant frequency of a circuit including said reactance. This invention relates further to means for indicating the weight of liquids, in which said apparatus is used as a speciiic gravity compensator in connection with conventional volume indicating means.

Such apparatus, when harnessed electrically to conventional volumetric indicating means, is especially useful in jet type aircraft to inform the pilot or other operating personnel of the weight of fuel present. Fuel tank gauges which involve means for temperature compensation, so as to indicate weight of fuel in the tank and hence the amount of available energy, instead of volume. are in production, and their performance is eX- cellent as long as they are used with fuel having a speciiic gravity within the range for which the gauges are designed. But, while such gauges can compensate for minor variations in speciiic gravity, they cannot give true indications of weight when the specic gravity of the fuel used can vary considerably. Most aircraft engines of the jet type will operate on fuels of widely varying speciiic gravities ranging from No. 1 fuel oil to high test gasoline. Such apparatus forms the subject matter of a copending application, Serial No. 302,298, filed August 2, 1952, which is a division of the present application.

This invention may also be used to indicate specific gravity only. Such a use is in determining the average specic gravity of liquid in a large storage tank. It is well known that when liquid is stored, the specific gravity of the liquid near the top is diierent from that near the bottom. By lowering the apparatus into the tank, the specific gravity near the bottom, near the top and at such intermediate points as may be desired, may be indicated by a pointer, by a series of lights, or otherwise.

Another use as a specific gravity indicator only is in indicating or recording the specific gravity of liquid flowing through a pipe line. The floats and the necessary electriccontacts can be housed in a separate unit and connected to the pipe line so that a portion of the liquid passing through the pipe line will pass slowly through the housing containing the iioats. Again the indication can be made by pointer indication, or by a series of lights, or otherwise.

An important feature of the invention is the use of a plurality of floats of predetermined avere age or bulk speciiic gravities graduated within the range of the specic gravities to be encountered, so that each iioat will sink or iioat independently of the others, depending upon the specic gravity of the liquid in which the floats are immersed, said floats being harnessed electrically to provide a progressive change in electrical resistance or reactance (either capacitive or inductive) as the specific gravity of the liquid varies. If a variable reactance is used, it, together with a reactance of opposite sign, may be connected to form a series-resonant circuit, the resonant frequency of which .is thus responsive to the specific gravity of the liquid. The resonant frequency may be determined by conventional means.

Accordingly, it is an object of the invention to provide accurate and simple apparatus for measurng and/or indicating the specific gravities of liquids.

The above and other objects and advantages will appear more fully hereinafter from consideration of the following description taken in conjunction with the accompanying drawings in which:

Figs. 1 and 2 illustrate an arrangement of a oat and its electric contacts in which the electric contacts and leads are isolated from the liquid;

3 is a side elevation partly in section on the line ii-t of Fig. li showing an embodiment of a float-controlled, magnetically operated switch in a specific gravity compensator which may be used in apparatus for indicating'the weight of liquid in a tank;

Fig. i is a View on line 4 4 of Fig. 3;

Fig. 5 is a side elevation of an installation of the embodiment of the invention shown in Figs. 3 and 4, showing a second float assembly behind the rst;

Fig. 6 illustrates diagrammatically a device for indicating the weight of liquid in a tank, in which a variable resistance type specic gravity gauge is used as a compensator with a variable inductance type fue-l quantity indicator;

Fig. '7 illustrates diagrammatically an arrangement for a variable inductance type specific gravity gauge; and

Fig. 8 illustrates diagrammatically an arrangement for a variable capacitance type specific gravity gauge.

The principle of this invention is based upon the use of a number of floats, four being shown in each embodiment illustrated in the drawings, but there may be any number. Each float is free to move up and down within certain predetermined limits and is intended at all times to be totally immersed in the liquid, the specific gravity of which is to be indicated or measured. Each float is differently weighted as represented, for example, by the cross hatched section 2-3 in Figs. 1 and 2, so that the floats in any set will rise or fall at progressively different liquidspecic gravities within the range of specific gravities to be indicated or recorded by the particular installation. When each float rises, it will either positively make or positively break (according to the arrangement of the particular installation) a circuit, which will be arranged as hereinafter noted, to cut in or out a "section of electrical impedance. The entire installation, therefore, is arranged to control the value of an electrical irnpedance in accordance with the specific gravity of the liquid in which all the 'floats collectively are immersed. The circuit including the electrical impedance in question may then be so constructed and arranged that the impedance will control an indicator or other means in proportion to the impedance value thereof, so as to indicate an electrical 'value which may be graduated in terms of specific gravity or which may be arranged to introduce an electrical value which is a function of the Vspecific gravity of the liquid into some other electric circuit means.

I a'ndII To adapt the invention, i. e., varying electrical impedance, whether it be resistance or reactance, through the use of a plurality of oats of different bulk specific gravities, for use in connection with fuel in an aircrafts fuel tank, or for use in connection with lother hazardous liquids, it is advisable to isolate the electrical portions, such as contacts and wires, from the liquid. Figs. 1 and 2 illustrate apparatus which accomplishes this object. We may referto Figs. l and 2 together, for they show the same apparatus in two diierent positions. A oat 3,60 of ferromagnetic material is totally immersed in or surrounded by the liquid (not shown), the specific gravity -of which is to be determined, and is free to move from the bottom `62 to the 'top 64 of a chamber 65. The float `|50 vwill bein the former position when its specific gravity is greater than that of the liquid and in the latter position when its specific gravity is less than that of the liquid. As the oat 60 rises, a magnetic coupling between the oat and amagnet :66 causes magnet 66 to rotate counter-clockwise (as shown) about a pivot point 68 on a bracket '|18 until a contact '50, carried on an arm 'l2 attached to magnet 66, touches a contact 14, thus closing a switch formed by contacts 'l0 and 14. Wires 16 may connect conta-cts I and 'Macross a portion of 'aresistance or a reactance (not shown), thus snorting out said 'portion when the float 60 has risen against the top 64 of its chamber 65, i. e., when the float 60 is of a specific gravity less than that of the liquid. It is to be understood that magnet 66, armI12, bracket 18, pivot point 68, contacts l0 and 'I4 and the wires 'i6 are housed in a sealed chamber 80, and are thus completely isolated from the liquid. With a plurality of installatio'ns as'shotvn in Figs-i but withffloa-ts of diiferent bulk specific gravities, the desired effect will be obtained as explained generally above.

III and IV Figs. 3 and 4, both partly in section, are a side elevation and a top view, respectively, of a floatcontrolled, magnetically operated switch, for use in a specific gravity gauge of the variable resistance or reactance type.

-It is to be understood that the float assembly shown in Figs. 3 and 4 is but one of several float assemblies in the -actual gauge, the floats being, as before, of diiferent bulk specic gravities graduated within the range of specific gravities to be encountered. Fig. 5 shows one assembly mounted behind another and will be best understood after `considering Figs. 3 and 4, in which a float arm |00 carries a spherical float |02 on one end, and a bifurcated box-like frame |04 on the other. Frame |04, which is supported on pivots 06, also supports a pair of magnets |08, one'being mounted on each end of frame |04. A switch housing, indicated generally at H0, is vcentrally disposed in frame |04 Vand is supported on a hollow 'pedestal ||4 which is mounted on a 'sealed housing |2 which may serve 'as a base for 'all the float assemblies. The switch housing 'comprises 'a sealed hollow drum having an annular shell i6 and double end plates |8 and |24 which are 'soldered together. Plates ||8 carry pivots |22 which support a switch rocker arm (to be described), While plates |24 carry the float arm pivots |06 in alignment with vpivots |22. All pivots or bearings may bejevvels, in order to reduce friction. This is desirable because lof the low power available. The jewels may also serve as insulators for the moving "parts inside the switch housing 0.

Centrally mounted on the pivot pins |22, inside the switch hou-sing ||0, is a switch rocker arm |26, box-like in structure, of electrically conductive material and provided 'with a pair of iron pole pieces |28, one on each end of the switch rcker arm |26. IIn rvertical cross-section, the iron pole pieces |28 resemble circular arcs, the centers of which are on the axis of the float arm pivots |06 and the Vpivot pins |22. The switch rocker arm |26 is provided with a pair of silver spacers or contacts |29. equidistant `from the axis ofthe float arm pivots |06 and thepivot fpins |22.

When the iioat |02 rises, duc to its bulk specie -gravity `being less than that `-of the liquid surrounding-it, Ythe-floatarm |00 rotates counterclockwise as seen in Fig. 3. `Magnetic coupling between the Amagnets 08 and the iron pole pieces |20 causesswiteh Arocker arm |26 likewise torotate counter-clockwise. Thus the switch rocker arm 26 follows the movement `of the float larm |00 -as the float |62 rises or falls. As a result, when -th'e float |02 rises, the p-air'of silver spacers |29 make contact (Fig. 5) one with each of a pair-of brushes |30-'anch'orediby rivets |32 on insulating kmaterial |34 in-the bottom of Vthe switch housing H0. Also anchored by the rivets |32 are the ends of lead 'wires |36, shown partially dotted, which Vare connected across 'part 'of the electric 'resistanceo'r 'reactance (not shown), the Value 1of 'which Iis to be responsive -to the specic gravity of the liquid. The resistanc'eior frcact'ance'may be located in the housing |2. The electrical connec'tiohsin the-case of Figs. 3 and 4- may be Vexactly the-saine as in the embodiments of 't-he-'ii-iventicn shown in Figs. 6,7-or=8 and hereinafter described.

Fig. 5 shows how a second float lassembly |42, as described in connection with Figs. 3 and 4, may be mounted behind a first float assembly |40 on the base |44. As many such assemblies may thus be mounted as desired or needed.

One of the important uses which can be made of the invention is as a specific gravity compens-ator in a gauge for indicating the weight of a liquid, such as gasoline, in a tank. To make such a gauge, the specific gravity compensator may be inserted in a circuit which would otherwise constitute a gauge for indicating merely the volume of liquid. Fig. 6 shows diagrammatically a circuit including a specific gravity compensator of the variable resistance type which can be used to indicate the weight of the liquid. The compensator, indicated diagrammatically at |50, is designed to cut in or out sections of a resistance as hereinafter described. The details of the switches, shown diagrammatically by way of example, could Ibe as illustrated in Figs. 1-2 or in Figs. 3-5, or as particularly described hereinafter in connection with Fig. 7. The compensator |50 controls the effective resistance value of a group of resistors |52, |54, |66 and |58, only `four being shown.

The fuel volume measuring element, indicated generally at |60, is a variable inductance coil |62, which is responsive to the liquid level by means of a float |64 connected to a permeable core |66 arranged to move into or out of the coil |62 as the float |64 rises or falls in response to changes in liquid level, the liquid not lbeing shown. This movement changes the inductance of the coil |62. It is to be noted that the liquid level responsive device, here the coil |62, in itself cornpensates for minor changes in specic gravity, but is ineffective when the specific gravity varies Widely, as it may from time to time in the case of fuel in the tanks of .jet type aircraft. The coil |62 is an element of a bridge circuit which includes, in addition to coil |62, a reference coil |68, and the secondary |12 of a, transformer |10 which may be energized by an audio frequency power Vsupply |16 connected across the primary |14 of the transformer |10.

secondary |12 and a point |00 between the coil |62 and the reference coil |68, and is fed to an output transformer |82. The secondary |64 of the transformer |32 is shunted by the resistors |52, |54, .|56 and |58, and lby `another resistor |86 of the specific gravity compensator |60. While shunt connections of the resistors have been shown, series connections or potentiometer connections may be used. A measuring circuit |88 is connected across the secondary |04 of the output transformer |82 and will detect the output of the ybridge circuit, and may compare it with a reference signal from an indicator |00 by a feed-back connection |02. The resulting signal may be amplified |by an amplifier |94 and be made to control the indicator |90. This, in effect, is `a, servo type circuit.

In operation, the bridge will be arranged to be in balance (that is, no output) when there is no liquid in the tank. Under this condition, all the floats of the compensator will be down, a condition which would correspond to having the tank full of very light liquid. However, since the output is zero, there will be no error in The output of the h bridge circuit is taken between a ta'p |10 on the the reading of the indicator |86. As the tank is lled, the bridge will become more and more unbalanced due to change in the inductance of the coil |62, and the output of the bridge to the measuring circuit will become progressively greater. If the specific gravity of the liquid now changes, the compensator |50 will further modify the output of the bridge by cutting out resistors or by adding them to the circuit depending on the direction of the variation. Thus, the final reading of the indicator will be a truer indication of the contents of the tank by weight than if the compensator |66 were omitted. It should be understood that the volume-responsive element |60 could just as well be capacitive, in which case the reference coil |68 would be replaced by a reference capacitance.

VII

The invention, as embodied in a variable reactance type specific gravity gauge, may be un derstood by referring to Fig. 7, in which any number of float assemblies collectively indicated at 2|0 (only four are shown) are near the bottom of a tank 2|2 containing liquid 2id, the speciiic gravity of which is to be determined. it will be understood that each oat operated switch could, for example, take the form of Figs. 1 2 or of Figs. 3 5. As illustrated, however, each float assembly comprises a float 2|6 or 2|6 oarried on one end or" an arm 2|3 pivoted at a point 220. Each iioat it` is shown at the lower end of its arc, while each neat 2|6 is shown at the upper end of its arc. On the other end of each arm 2|@ is an electric contact 222, which is part of a switch indicated generally at 224, the other contact being shown at 226. When a float 2|6 travels upwardly along its arc, 'due to its bulk specific gravity being less than that of liquid 2id, its arm 2|8 rotates counterclocirwise (as seen in Fig. '7) until contact 222 touches contact thereby closing switch 224. Each switch 224 is connected across a respectively corresponding predetermined portion 225 of an inductance 22S,

so that when a switch 224 is closed, its corre sponding predetermined portion 225 of inductance '228 is shorted out. Coil 228 is shown as a singie coil tapped at various sections, but itv will be understood that a number of separate coils may be used. The operation just described may be repeated as many times as there are floats 2|6 and 2|6', each noat 2 6 or 2 i 6' being weighted corresponding to a different bulk specific gravity, so that the specic gravity of the liquid 2|4 will be less than that of the last float 2 i6 at the end of its arc and greater than that of the first float 2|6 at the upper end of is arc. rihus, the amount of the inductance 226 not shorted out corresponds to a definite specific gravity of the liquid 2M, the greater being the specific gravity of the liquid, the smaller being the effective value of the inductance 228. Coil 223 is connected in series with a condenser 230, which together form a series-resonant circuit, 'the resonant frequency of which is a definite function of the value of the inductance 226, and is given by the formula 21m/LC frequency oscillator 232, shown in block form, which may be so constructed that it will oscillate at said resonant frequency, as is well known in the art. The oscillator 232 is energized by a power supply 234. The frequency of oscillation of oscillator 232 may be measured by any con-- venient form of frequency meter, shown in block form at 236, which may be calibrated to indicate specic gravity directly.

In operation, the specific gravity-sensitive floats 216 and 216 may be placed in tank 212 for the purpose of determining the specific gravity of the liquid 2M therein. liquid '2M is of an average specic gravity, the system can be adjusted so that, for example, half the floats 2l6 are at the bottoms of their arcs and the other half are at the tops of their arcs. This means that half the switches 226 will be open and the other half will be closed` Thus some of the turns of coil 228 will be snorted out, causing the oscillator 232 to generate a signal of a definite xed frequency. Ii a lighter liquid is now placed in the tank 2&2, the noat 2|6 having the greatest bulk specic gravity will also sink, thereby opening its switch and increasing the inductance oi the coil 226, thus causing the oscillator 232 to generate a signal of lower frequency. However, if the substituted liquid hasa greater specic gravity than does the original liquid 2 I 4, the float 2 i 6 having the smallest bulk specific gravity will rise, thereby closing its switch 224. This shorts out more of the coil 22B and decreases its inductance, thereby causing the oscillator 232 to generate a signal of greater frequency. The frequency meter 236 can then be conveniently calibrated to indicate specic gravity directly.

VIII

The circuit shown in Fig. 8 is in general similar to that of Fig. 1, in that it contains a seriesresonant circuit including inductive and' capacitive elements. However, in this case, instead of varying the inductive element responsive to changes in the specific gravity of the liquid under test, as done in the circuit of Fig. '1 the capacity is changed. The arrangement of the floats shown in Fig. 8 at 26D and 268 and their corresponding switches, shown generally and diagrammatically in Fig. 8 at 262, is exactly the same as in the apparatus shown in Fig. '7 and need not be described again. Again, the float assembly is illustrated near the bottom 264 oi a tank 266 containing the liquid 2&8 under test. The series-resonant circuit in the case of Fig. 8 starts with a lead wire 21d from a variable frequency oscillator 212, and comprises a fixed inductance 214 in series with a condenser 216, which is connected by a lead 21| back into the oscillator 212. The oscillator 212y again is energized by a power supply 218, but as a variation from the circuits described in connection with Fig. 7, the oscillator 212 is arranged to feed into a frequency discriminator 236 from which suitable currents may be derived to operate a ratiometer 282 and a pointer (not shown).

One side of each switch 262 is connected to the lead 21| and a condenser 284 is connected in series with the other side of each switch 262 respectively. The side of each condenser 2.86 remote from its corresponding switch 262 is connected to the end of the coil 214 remotefrom the oscillator 21,2. Thus when a float 2.66 is at the top of its arcdue to itsgspeciflcgravity-being less than. that of the.- liquid 268, its; corresponding;

If it be assumed that the 8 switch 262 is closed. With the switch in this condition, the corresponding condenser 284 will be connected in parallel with the condenser 216.

In operation, the apparatus may be adjusted so that for a liquid of average specific gravity, half the floats, i. e. the oats 260 will be at the bottoms of their arcs and half the floats, i. e. the floats 260 will be at the tops of their arcs. If a liquid of greater than average specic gravity is substituted, one of 'the iioats 26B will rise, thus closing its. switch 262, and connecting its corresponding condenser 284 in parallel with the condenser 216. Thereby, the overall capacity of the series-resonant circuit including the coil 2.14 and the condenser 216 is increased, since when two condensers are connected in parallel, the equivalent series capacitance is the sum of the capacitances of the two condensers. Conversely, if a liquid of less than average specific gravity is substituted, one of the floats 266 will sink, thus opening its switch 262 and decreasing the capacitance of the series-resonant circuit by the value of its corresponding condenser. As is the case in the circuits shown in Fig. 7, these changes in the specic gravity of the liquid under test are reected in changes in the frequency of the signal generated by the oscillator 212. When the capacitance increases (due to an increase in specific gravity), the generated frequency decreases, and vice versa. The-se frequency changes are in turn reflected by changes in the indicator readings, as in the other circuits.

The described apparatus will be seen to provide a simple, accurate and reliable measurement and indication of the speciiic gravity of a liquid in accordance with the objectives of the present invention, but it is to be understood that the invention is not limited to the specific embodiments herein illustrated and described, but may be used in other ways without departure from its spirit as dened by the following claims.

I claim:

l. Apparatus for measuring the specific gravity of a liquid within a predetermined range, comprising a plurality of floats having respectively diierent bulk specific gravities graduated within said range, each of said oats having a substantially predetermined range of movement and being mounted in the liquid, the specic gravity of which is to bev measured, so as to be adjacent to the top or bottom, of its range of movement respectively as its bulk specific gravity is less or greater than that of the liquid; each of said floats having movable therewith nrst ferromagnetic material, a plurality of switches, each including contact means and second ferromagnetic material, each of said.l switches being responsive to the position of one-of said floats respectively by means of magnetic coupling between said rst and sec- 0nd ferromagnetic material; an electrical impedance having a section controlled respectively by each of said switches, so that each impedance section will be cut in or out depending on the position of the oneof said floats respectively associated therewith as aforesaid, whereby the resulting electrical value of said impedance is a predetermined function of the specific gravity to be measured; and indicating means controlled at least in part by said resulting electrical value of said impedance, so that the indication aiforded by said indicating means will be a. function of the specific gravity of theliqnid being measured'.

2. Apparatusaccording tolclaimY l, whereinasaid' electrical impedance' is a. resistor.

3. Apparatus according to claim 1, wherein said electrical impedance is an electrical reactance means.

4. Apparatus according to claim 1, wherein each of said floats is secured to one end of a float ann, each said float arm carrying a bifurcated portion spaced from its respective float and two magnets comprising said rst ferromagnetic material and mounted in spaced relationship within said bifurcated portion, wherein each o-f said switches is disposed in a liquid-tight housing fixed in position, each said housing being positioned between its respective magnets, each of said switches being responsive to the position of its respective float, each said housing bearing on its outside centrally disposed rst pivot means carrying said housings respective float arm, each said,switch including a rocker arm having said second ferromagnetic material secured thereto and rotatably mounted on second pivot means mounted on the inside of said housing containing said switch, said second pivot means being axially aligned with said rst pivot means, said rocker arms position being responsive to the rotative position of said magnets due to magnetic coupling between said magnets and said second ferromagnetic material, rst contact means mounted on said rocker arm, and second contact means mounted on insulating material within said housing and adapted to be engaged by said first contact means.

5. Apparatus according to claim 1, wherein each of said oats is secured to a float arm, each said oat arm carrying said first ferromagnetic material, wherein each of said switches is disposed in a liquid-tight housing, said housing for each switch being positioned adjacent to said first ferromagnetic material, said float arm being rotatably mounted on said housing, each of said switches being responsive to the position of its respective float, each of said switches including a rocker arm bearing first contact means and having said second ferromagnetic material secured thereto, said rocker arms being positioned in response to the rotative position of said first ferromagnetic material due to magnetic coupling between said rst and second ferromagnetic material, and second contact means for each switch adapted to be engaged by said first contact means.

6. Apparatus according to claim l, wherein said electrical impedance comprises rst variable reactance means responsive to changes in the positions of said floats, a second reactance means of opposite sign from said first reactance means; wherein said indicating means is a specific gravity indicator; and further comprising a circuit connecting said first and second reactance means in series and including connections from said reactance means to said indicator, said circuit including means for measuring the series-resonant frequency of the series-connected reactance means aforesaid, and said indicator being controlled by the measured frequency of said circuit,

so as to indicate the specific gravity of said liquid.l

'7 Apparatus according to claim l, wherein said electrical impedance comprises a variable electrical inductance responsive to changes in the positions of said floats, and an electrical capacitor connected in series with said inductance to form a series-resonant circuit; and wherein said indicating means comprises an indicator, and means responsive to the series-resonant frequency of said resonant circuit for controlling said indicator to indicate a value which is a function of said frequency and which is directly characteristic of the specific gravity of said liquid.

8. Apparatus according to claim 1, wherein said electrical impedance comprises electrical capacitance means including a yplurality of capacitors, current flow through which is controlled by each of said floats respectively, a series-resonant circuit including all said capacitors in parallel and a series-connected inductance; and wherein said indicating means comprises an indicator connected in said circuit and responsive to the seriesresonant frequency thereof, so that said indicator will indicate a value directly characteristic of the specic gravity of said liquid.

References Cited in the file of this patent UNITED STATES PATENTS 

